The present invention is directed to the surface treatment of medical devices including ophthalmic lenses, stents, implants and catheters. In particular, the present invention is directed to a simple, low cost method of modifying the surface of a medical device to increase its wettability.
Medical devices such as ophthalmic lenses made from silicone-containing materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Regardless of their water content, both non-hydrogel and hydrogel silicone medical devices tend to have relatively hydrophobic, non-wettable surfaces that have a high affinity for lipids. This problem is of particular concern with contact lenses.
Those skilled in the art have long recognized the need for modifying the surface of such silicone contact lenses so that they are compatible with the eye. It is known that increased hydrophilicity of the contact lens surface improves the wettability of the contact lenses. This in turn is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens""s susceptibility to deposition, particularly the deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended wear lenses (i.e. lenses used without daily removal of the lens before sleep), the surface is especially important, since extended wear lens must be designed for high standards of comfort and biocompatibility over an extended period of time.
Silicone lenses have been subjected to plasma surface treatment to improve their surface properties, e.g., surfaces have been rendered more hydrophilic, deposit resistant, scratch-resistant, or otherwise modified. Examples of previously disclosed plasma surface treatments include subjecting contact lens surfaces to a plasma comprising an inert gas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942; and 4,214,014); various hydrocarbon monomers (see, for example, U.S. Pat. No. 4,143,949); and combinations of oxidizing agents and hydrocarbons such as water and ethanol (see, for example, WO 95/04609 and U.S. Pat. No. 4,632,844). U.S. Pat. No. 4,312,575 to Peyman et al. discloses a process for providing a barrier coating on a silicone or polyurethane lens by subjecting the lens to an electrical glow discharge (plasma) process conducted by first subjecting the lens to a hydrocarbon atmosphere followed by subjecting the lens to oxygen during flow discharge, thereby increasing the hydrophilicity of the lens surface.
U.S. Pat. Nos. 4,168,112, 4,321,261 and 4,436,730, all issued to Ellis et al., disclose methods for treating a charged contact lens surface with an oppositely charged ionic polymer to form a polyelectrolyte complex on the lens surface that improves wettability.
U.S. Pat. No. 4,287,175 to Katz discloses a method of wetting a contact lens that comprises inserting a water-soluble solid polymer into the cul-de-sac of the eye. The disclosed polymers include cellulose derivatives, acrylates and natural products such as gelatin, pectins and starch derivatives.
U.S. Pat. No. 5,397,848 to Yang et al. discloses a method of incorporating hydrophilic constituents into silicone polymer materials for use in contact and intra-ocular lenses.
U.S. Pat. Nos. 5,700,559 and 5,807,636, both to Sheu et al., discloses hydrophilic articles (for example, contact lenses) comprising a substrate, an ionic polymeric layer on the substrate and a disordered polyelectrolyte coating ionically bonded to the polymeric layer.
U.S. Pat. No. 5,705,583 to Bowers et al. discloses biocompatible polymeric surface coatings. The polymeric surface coatings disclosed include coatings synthesized from monomers bearing a center of positive charge, including cationic and zwitterionic monomers.
European Patent Application EP 0 963 761 Al discloses biomedical devices with coating that are said to be stable, hydrophilic and antimicrobial, and which are formed using a coupling agent to bond a carboxyl-containing hydrophilic coating to the surface by ester or amide linkages.
Thus, it is desired to provide a silicone hydrogel contact lens with an optically clear, hydrophilic surface film that will not only exhibit improved wettability, but which will generally allow the use of a silicone hydrogel contact lens in the human eye for extended period of time. In the case of a silicone hydrogel lens for extended wear, it would be desirable to provide a contact lens with a surface that is also highly permeable to oxygen and water. Such a surface treated lens would be comfortable to wear in actual use and would allow for the extended wear of the lens without irritation or other adverse effects to the cornea. It would be desirable to manufacture such a surface treated lens without the need for an oxidation step such as plasma treatment or corona discharge treatment.
The present invention is directed to a method for improving the wettability of a medical device, comprising the steps of:
(a) providing a medical device formed from a monomer mixture comprising a hydrophilic monomer and a silicone-containing monomer, wherein said medical device has not been subjected to a surface oxidation treatment, and
(b) contacting a surface of the medical device with a solution including a polymer or copolymer of (meth)acrylic acid, whereby the polymer or copolymers of (meth)acrylic acid forms a complex with the hydrophilic monomer on the contact lens surface without a surface oxidation treatment step and without the addition of a coupling agent.
In a preferred embodiment, the meth(acrylic) acid polymer or copolymer comprises acid content of at least 40 mole percent, more preferably at least about 50 mole percent.
The method of the invention requires neither surface oxidation treatment step nor the addition of a coupling agent. The term xe2x80x9ccoupling agentxe2x80x9d means an entity other than the medical device or the hydrophilic coating material that forms a linkage between the surface of the medical device and the hydrophilic coating material. Examples of linkages provided by coupling agents include ester linkages and amide linkages.